Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry. The processing circuitry receives coded information of a block that is encoded in a palette based coding mode. The block is a beginning of a predefined coding region that includes one or more coding tree units (CTUs). The processing circuitry further determines a palette for the block independently of palette information of one or more previously decoded blocks of the palette based coding mode, and decodes pixels of the block based on the coded information of the block and the determined palette for the block.

INCORPORATION BY REFERENCE

This present disclosure is a Continuation of U.S. patent applicationSer. No. 16/940,842, filed Jul. 28, 2020, which claims the benefit ofpriority to U.S. Provisional Application No. 62/883,900, “PALETTEPREDICTOR LIST RESET” filed on Aug. 7, 2019, which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chromimancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has specific bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 shows a schematic (201) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. The processingcircuitry receives coded information of a block that is encoded in apalette based coding mode. The block is a beginning of a predefinedcoding region that includes one or more coding tree units (CTUs). Theprocessing circuitry further determines a palette for the blockindependently of palette information of one or more previously decodedblocks of the palette based coding mode, and decodes pixels of the blockbased on the coded information of the block and the determined palettefor the block.

In some embodiments, the processing circuitry resets a palette predictorlist that stores the palette information of the one or more previouslydecoded blocks, to a zero state in response to the block being thebeginning of the coding region that includes the one or more CTUs.

In an example, the block is the beginning of a CTU. In another example,the block is the beginning of a CTU row. In another example, the blockis the beginning of a tile. In another example, the block is thebeginning of a slice.

In an embodiment, the block is a beginning of a CTU row, and theprocessing circuitry resets a palette predictor list that stores thepalette information of the one or more previously decoded blocks, to azero state in response to an enabling of wavefront parallel processing(WPP).

In another embodiment, the block is a beginning of a CTU row, and theprocessing circuitry resets a palette predictor list according to apalette initializer in response to an enabling of wavefront parallelprocessing (WPP).

In another embodiment, the block is a beginning of a CTU, and theprocessing circuitry resets a palette predictor list according to apalette predictor initializer in response to an enabling of wavefrontparallel processing (WPP).

In another embodiment, the block is a beginning of a first predefinedcoding region, and the processing circuitry determines the palette forthe block independently of palette information of blocks in a secondpredefined coding region that is decoded in parallel with the firstpredefined coding region.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 2 is an illustration of exemplary intra prediction directions.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows a partition example in a video according to someembodiments of the disclosure.

FIG. 10 shows another partition example in a video according to someembodiments of the disclosure.

FIG. 11 shows another partition example in a video according to someembodiments of the disclosure.

FIG. 12 shows a flow chart outlining a process example according to someembodiments of the disclosure.

FIG. 13 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531)(e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block: that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y. and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CiCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5. Brieflyreferring also to FIG. 5, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels. 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7.

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8.

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403). (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

According to some aspects of the disclosure, a coding mode that isreferred to as palette based coding mode can be used in addition to theinter prediction mode and the intra prediction mode. The presentdisclosure provides techniques to improve coding efficiency of palettebased coding mode.

In some embodiments, a palette is defined as a lookup table of entriesthat associate indices with pixel values. In some examples, a pixelvalue includes one or more values corresponding to color components. Inan example, a pixel value can include three values respectivelyrepresenting three color components. In another example, for amonochrome palette, a pixel value includes a value representing a singlecolor component.

In some embodiments, a block of pixels can be encoded based on thepalette, and the coding mode using the palette is referred to as palettebased coding mode. The palette based coding mode is adopted in somevideo coding standards, such as VVC and the like.

According to some embodiments, the palette based coding mode is astandalone coding mode. In an embodiment, the palette based coding modeis implemented as a coding unit (e.g., palette based encoder, palettebased decoder and the like) that is separately from the intra encoder(722), the inter encoder (730), the intra decoder (872), the interdecoder (870). In an example, the palette based coding mode isimplemented as separate hardware circuitry from the intra encoder (722),the inter encoder (730), the intra decoder (872), the inter decoder(870). In another example, the palette based coding mode is implementedas a separate software module from software modules for the intraencoder (722), the inter encoder (730), the intra decoder (872), theinter decoder (870). The software module for palette based coding modeand other software modules can be executed by a same processor ordifferent processors.

According to some aspects of the disclosure, a palette based coding modegenerally includes two parts: a first part of coding methods for thepalette and a second part of coding methods for the samples using thepalette. The first part can include major color selection and palettecoding. The second part can include palette index coding, run lengthcoding, and escape pixel coding.

In some examples, a palette based encoder can encode a block of videodata by determining the palette for the block (e.g., coding the paletteexplicitly, predicting the palette, a combination of signaling andpredicting, and the like), locating an entry in the palette to representone or more of the pixel values, and encoding the block with indexvalues that indicate the entries in the palette used to represent thepixel values of the block. In some examples, the palette based encodermay signal the palette and/or the index values in an encoded bitstream.In turn, the palette based decoder may obtain, from an encodedbitstream, a palette for a block, as well as index values for theindividual pixels of the block. In some other examples, the palette canbe predicted, and the palette based encoder can signal the index valuesin the encoded bitstream without signaling the palette and the palettebased encoder can predict the palette and receive the index values inthe encoded bitstream. Then, the palette based decoder can relate theindex values of the pixels to entries of the palette that provide pixelvalues. The palette based decoder than reconstruct the various pixels ofthe block based on the pixel values associated with the index values.

Some aspects of the present disclosure provide techniques for the firstpart related to palette coding process.

According to some embodiments, a palette may include the most dominantpixel values in a given block. For example, the most dominant pixelvalues may include the one or more pixel values that occur mostfrequently within the given block. Additionally, in some examples, athreshold value (e.g., number of pixels having the pixel value) can beused to determine whether a pixel value is to be included as one of themost dominant pixel values in the block.

In some embodiments, a histogram based algorithm is used to classifypixel values of pixels in a block in order to form a palette. In someexamples, the most significant L peak values in the histogram can beselected as major colors (L is a positive integer). In an example, thepixel values that are close to a major color can be quantized to themajor color. In some examples, pixels which do not belong to any majorcolors are referred to as escape pixels. The escape pixels can bequantized before coding. In some embodiments, for lossless coding, thequantization processes are not performed.

Further, in some embodiments, for each pixel, a color index is assignedto indicate which color the pixel belongs to. In some examples, if Lmajor colors are used, 0 to (L−1) can be used as color indices for themajor colors, and 0 to (L−1) can be referred to as a major color set.For those pixels whose major color indexes do not exist, a special index(e.g., index N other than 0 to (L−1)) is assigned to them and thesepixels are called ‘escaped pixels’.

Generally, the palette is implemented as a color lookup table. The colorlookup table includes a plurality of entries. Each entry associates acolor index with a color (e.g., major color). In some examples, a singlepalette is used to code both luma and chroma components. Each entry canrepresent a specific RGB(YUV) color using three color components. Forexample, a palette can have entry 1 with (R, G, B)=(0, 0, 0) thatrepresents pure black color, and can have entry 0 with (R, G, B)=(2, 10,200) that represents a bluish color. It is noted that when the videoformat is 420, the chroma plane are up sampled to generate the colorlookup table for palette.

In some embodiments, palette based coding is performed on a CU basis. Inan example, for a current CU, a color lookup table is derived whichincludes the most dominant pixel values in the current CU. In someexamples, the size and the elements of the color lookup table can betransmitted. In some other examples, the size and the elements of thecolor lookup table can be predictively coded using the size and/or theelements of the color lookup table of other CUs.

According to some aspects of the disclosure, palette prediction can beperformed based on a palette predictor list. In an example, a palettepredictor list can include multiple palettes that are used for otherCUs. To code the current palette using the palette predictor list as areference, a binary vector is used to indicate whether each palette inthe palette predictor list is reused in the current palette.

In some examples (e.g. HEVC SCC), a palette predictor list stores thepreviously coded palette entries as references to predict the currentpalette. The palette predictor list is updated after each palette modeCU. In an example, the palette predictor list operates in a similarmanner as a least recently used cache. The latest palette can beinserted at the beginning of the palette predictor list and the entriesfrom the farthest CUs in scan order are discarded if the list sizeexceeds a threshold. In an embodiment, the upper bound of the size ofthe palette predictor list is (directly or indirectly) signaled in theSPS header. For example, the palette predictor list can have roughlytwice the size of the size limit for a palette. In some examples, thepalette predictor list is also referred to as history palette predictorlist (HPPL).

In some embodiments, entries in the palette prediction list can haverespectively reuse flag. When a reuse flag for an entry is true (e.g.,“1”), the entry is referred to as a reused entry. Color components ofthe reused entries in the palette prediction list can be copied to thecolor lookup table of the current palette. The reused entries are placedat the beginning of the current palette in a manner to maintain theirorder in the palette predictor list. The reused entries in the currentpalette can be followed by new palette entries which are not in thepalette predictor list. The new palette entries can be signaled. Eachnew palette entry can include for example three color components.

In some embodiments, a palette initializer with predefined entries canbe used to initialize the palette predictor list. The use of paletteinitializer can result in improved coding efficiency in some scenarios.A palette initializer can be signaled, for example in the pictureparameter set (PPS), in the sequence parameter set (SPS), and the like.

According to an aspect of the disclosure, at the boundaries of slicesand tiles, palette prediction based on neighboring CUs may be notefficient, thus slices and tiles can result in substantial codingefficiency loss when the palette predictor list is reset at the sliceand tile boundaries, since after the reset, it takes time to rebuild thepalette predictor list. In some examples, when the palette initializerwith predefined entries is used to initialize the palette predictorlist, the coding efficiency in such a scenario can be improved. Apalette initializer can be signaled in the picture parameter set (PPS)or the sequence parameter set (SPS). In an example, each of the threecolor components of an entry in the palette initializer is signaled. Insome examples, at the start of a slice or a tile, the palette predictorlist is initialized by the palette initializer. The entries of thepalette predictor list also have three color components. In an example,each entry of the palette predictor list can be copied from the palettepredictor initializer.

In some examples, in the palette based coding mode, the palettepredictor list is reset at the beginning of every slice. When parallelprocessing is applied to the palette based coding mode, multiple CTUrows are encoded in parallel. The construction of the palette predictorlist causes coding of a CTU row depend on previous CTU row. Some aspectsof the disclosure can enable true parallel processing of CTU rows andimprove coding efficiency.

The proposed methods may be used separately or combined in any order.Further, each of the methods (or embodiments), encoder, and decoder maybe implemented by processing circuitry (e.g., one or more processors orone or more integrated circuits). In one example, the one or moreprocessors execute a program that is stored in a non-transitorycomputer-readable medium. In the following, the term block may beinterpreted as a prediction block, a coding block, or a coding unit,i.e. CU.

According to some aspects of the disclosure, a picture (or frame) in avideo can be divided into coding regions and processed by codingregions. The coding regions can be defined (or predefined) according toany suitable techniques. In some embodiments, the coding regions can beprocessed (e.g., encoded or decoded) independently. Thus, in someexamples, the coding regions can be processed in parallel for fastprocessing.

FIG. 9 shows an example of a picture (900) in a video according to someembodiments of the disclosure. The picture (900) is partitioned intoCTUs of the same square size for compression. In some examples, CTU rowsare defined as coding regions. A CTU row includes a plurality of CTUs inthe same row.

FIG. 10 shows an example of a picture (1000) in a video according tosome embodiments of the disclosure. The picture (1000) is partitionedinto CTUs of the same square size for compression. In the FIG. 10example, tiles are defined as coding regions. Tiles have rectangularshape, and are defined by number of CTUs for the width and height. Forexample, the size of the tiles in FIG. 10 has a width of three CTUs anda height of two CTUs.

FIG. 11 shows an example of a picture (1100) in a video according tosome embodiments of the disclosure. The picture (1100) is partitionedinto CTUs of the same square size for compression. In the FIG. 11example, slices are defined as coding regions. The slices are definedaccording to raster scan order. Each slice can includes a plurality ofCTUs in the raster scan order.

According to some aspects of the disclosure, the palette predictor listcan be reset to zero state or emptied at the beginning of a codingregion. In an example, to reset the palette predictor list to the zerostate, the size of the palette predictor list size will be set to zero.Further, the entries in the palette predictor list are also set to zero.

It is noted that the coding region can be any suitable coding region. Inan example, the palette predictor list can be reset to zero state oremptied when the current CU is the beginning of a CTU. In anotherexample, the palette predictor list can be reset to zero state oremptied when the current CU is the beginning of a tile. In anotherexample, the palette predictor list can be reset to zero state oremptied when the current CU is the beginning of a CTU row. In anotherexample, the palette predictor list can be reset to zero state oremptied when the current CU is the beginning of a slice.

In some embodiments, CTU rows can be processed in parallel in awavefront manner when wavefront parallel processing (WPP) operation isenabled. In some examples, the palette predictor list is reset to a zerostate at the beginning of each CTU row when WPP operation is enabled.

In some embodiments, when the palette predictor list is in the zerostate, the palette of the block can be signaled in the coded bitstream.In some other embodiments, the palette predictor list can be initializedaccording to a palette initializer. The palette initializer can besignaled at high level syntax, such as at PPS or SPS, or can bepredefined and known by both encoder and decoder.

In an embodiment, the palette predictor list can be initializedaccording to the palette initializer when the current CU is at thebeginning of a CTU row.

In another embodiment, when WPP operation is enabled, the palettepredictor list can be initialized according to the palette initializerwhen the current CU is at the beginning of a CTU row.

In another embodiment, the palette predictor list can be initializedaccording to the palette initializer when the current CU is at thebeginning of a CTU.

In another embodiment, the palette predictor list can be initializedaccording to the palette initializer when the current CU is at thebeginning of a tile.

In another embodiment, the palette predictor list can be initializedaccording to the palette initializer when the current CU is at thebeginning of a slice.

FIG. 12 shows a flow chart outlining a process (1200) according to anembodiment of the disclosure. The process (1200) can be used in thereconstruction of a block. In various embodiments, the process (1200)are executed by processing circuitry, such as the processing circuitryin the terminal devices (310), (320), (330) and (340), the processingcircuitry that performs functions of the video encoder (403), theprocessing circuitry that performs functions of the video decoder (410),the processing circuitry that performs functions of the video decoder(510), the processing circuitry that performs functions of the videoencoder (603), and the like. In some embodiments, the process (1200) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1200). The process starts at (S1201) and proceeds to(S1210).

At (S1210), coded information of a block is received from a codedbitstream. The block is encoded in a palette based coding mode. Theblock is a beginning of a predefined coding region that includes one ormore coding tree units (CTUs). In an example, the block is the beginningof a CTU. In another example, the block is the beginning of a CTU row.In another example, the block is the beginning of a tile. In anotherexample, the block is the beginning of a slice.

At (S1220), a palette for the block is determined independently ofpalette information of one or more previously decoded blocks of thepalette based coding mode.

In some embodiments, a palette predictor list that stores the paletteinformation of the one or more previously decoded blocks, is reset to azero state in response to the block being the beginning of the codingregion that includes the one or more CTUs. In some examples, the paletteof the block is signaled in the coded bitstream, the palette of theblock can be extracted from the coded bitstream. In some examples, thepalette predictor list is reset according to a palette initializer, andthen the palette of the block is determined based on the palettepredictor list.

In an embodiment, the block is a beginning of a CTU row, a palettepredictor list that stores the palette information of the one or morepreviously decoded blocks, is reset to a zero state in response to anenabling of wavefront parallel processing (WPP).

In another embodiment, the block is a beginning of a CTU row, and apalette predictor list is reset according to a palette initializer inresponse to an enabling of wavefront parallel processing (WPP). Thepalette initializer can be signaled in a high level syntax, such as PPS,SPS and the like.

In another embodiment, the block is a beginning of a CTU, and a palettepredictor list is reset according to a palette initializer in responseto an enabling of wavefront parallel processing (WPP).

In some embodiments, the block is a beginning of a first predefinedcoding region, and the palette for the block is determined independentlyof palette information of blocks in a second predefined coding regionthat is decoded in parallel with the first predefined coding region.

At (S1230), pixels of the block are decoded based on the codedinformation of the block and the determined palette for the block. In anexample, the coded information of the block includes indices for pixels.The palette of the block includes a lookup table that associates theindices with pixel values (e.g., values for color components). Based onthe lookup table and the indices, pixel values can be determined. Then,the process proceeds to (S1299) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 13 shows a computersystem (1300) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 13 for computer system (1300) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1300).

Computer system (1300) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1301), mouse (1302), trackpad (1303), touchscreen (1310), data-glove (not shown), joystick (1305), microphone(1306), scanner (1307), camera (1308).

Computer system (1300) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1310), data-glove (not shown), or joystick (1305), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1309), headphones(not depicted)), visual output devices (such as screens (1310) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability-some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output: virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1300) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1320) with CD/DVD or the like media (1321), thumb-drive (1322),removable hard drive or solid state drive (1323), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1300) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1349) (such as, for example USB ports of thecomputer system (1300)); others are commonly integrated into the core ofthe computer system (1300) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1300) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1340) of thecomputer system (1300).

The core (1340) can include one or more Central Processing Units(CPU)(1341), Graphics Processing Units (GPU) (1342), specializedprogrammable processing units in the form of Field Programmable GateAreas (FPGA) (1343), hardware accelerators for certain tasks (1344), andso forth. These devices, along with Read-only memory (ROM) (1345),Random-access memory (1346), internal mass storage such as internalnon-user accessible hard drives, SSDs, and the like (1347), may beconnected through a system bus (1348). In some computer systems, thesystem bus (1348) can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus (1348), or through a peripheral bus (1349). Architectures for aperipheral bus include PCI, USB, and the like.

CPUs (1341), GPUs (1342), FPGAs (1343), and accelerators (1344) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1345) or RAM (1346). Transitional data can be also be stored in RAM(1346), whereas permanent data can be stored for example, in theinternal mass storage (1347). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1341), GPU (1342), massstorage (1347), ROM (1345). RAM (1346), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1300), and specifically the core (1340) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1340) that are of non-transitorynature, such as core-internal mass storage (1347) or ROM (1345). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1340). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1340) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1346) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1344)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video encoding, comprising:receiving pixel values of a block in a current picture to be coded in apalette based coding mode, the block being at a beginning of apredefined coding region that includes one or more coding tree units(CTUs); resetting, by processing circuitry, a palette predictor listthat stores palette information of one or more previously coded blocksof the palette based coding mode to a zero state in response to theblock being at the beginning of the coding region that includes the oneor more CTUs; determining, by the processing circuitry, a palette forthe block independently of the palette information of the one or morepreviously coded blocks of the palette based coding mode; and encoding,by the processing circuitry, the pixel values of the block based on thedetermined palette for the block.
 2. The method of claim 1, wherein theblock is the beginning of at least one of a CTU, a CTU row, a tile, anda slice.
 3. The method of claim 1, wherein the predefined coding regionis a CTU row, and the resetting is performed after enabling of wavefrontparallel processing (WPP).
 4. The method of claim 1, wherein thepredefined coding region is a CTU row, and the resetting is performedaccording to a palette predictor initializer after enabling of wavefrontparallel processing (WPP).
 5. The method of claim 1, wherein thepredefined coding region is a CTU, and the resetting is performedaccording to a palette predictor initializer after enabling of wavefrontparallel processing (WPP).
 6. The method of claim 1, wherein thedetermining the palette for the block is performed independently ofpalette information of blocks in another predefined coding region thatis decodable in parallel with the predefined coding region.
 7. Anapparatus for video encoding, comprising: processing circuitryconfigured to: receive pixel values of a block in a current picture tobe coded in a palette based coding mode, the block being at a beginningof a predefined coding region that includes one or more coding treeunits (CTUs); reset a palette predictor list that stores paletteinformation of one or more previously coded blocks of the palette basedcoding mode to a zero state in response to the block being at thebeginning of the coding region that includes the one or more CTUs;determine a palette for the block independently of the paletteinformation of the one or more previously coded blocks of the palettebased coding mode; and encode the pixel values of the block based on thedetermined palette for the block.
 8. The apparatus of claim 7, whereinthe block is the beginning of at least one of a CTU, a CTU row, a tile,and a slice.
 9. The apparatus of claim 7, wherein the predefined codingregion is a CTU row, and the processing circuitry is configured to resetthe palette predictor list after enabling of wavefront parallelprocessing (WPP).
 10. The apparatus of claim 7, wherein the predefinedcoding region is a CTU row, and the processing circuitry is configuredto reset the palette predictor list according to a palette predictorinitializer after enabling of wavefront parallel processing (WPP). 11.The apparatus of claim 7, wherein the predefined coding region is a CTU,and the processing circuitry is configured to reset the palettepredictor list according to a palette predictor initializer afterenabling of wavefront parallel processing (WPP).
 12. The apparatus ofclaim 7, wherein the processing circuitry is configured to determine thepalette for the block independently of palette information of blocks inanother predefined coding region that is decodable in parallel with thepredefined coding region.
 13. A non-transitory computer-readable mediumstoring instructions which when executed by a computer cause thecomputer to perform: receiving pixel values of a block in a currentpicture to be coded in a palette based coding mode, the block being at abeginning of a predefined coding region that includes one or more codingtree units (CTUs); resetting a palette predictor list that storespalette information of one or more previously coded blocks of thepalette based coding mode to a zero state in response to the block beingat the beginning of the coding region that includes the one or moreCTUs; determining a palette for the block independently of the paletteinformation of the one or more previously coded blocks of the palettebased coding mode; and encoding the pixel values of the block based onthe determined palette for the block.
 14. The non-transitorycomputer-readable medium of claim 13, wherein the block is the beginningof at least one of a CTU, a CTU row, a tile, and a slice.
 15. Thenon-transitory computer-readable medium of claim 13, wherein thepredefined coding region is a CTU row, and the resetting is performedafter enabling of wavefront parallel processing (WPP).
 16. Thenon-transitory computer-readable medium of claim 13, wherein thepredefined coding region is a CTU row, and the resetting is performedaccording to a palette predictor initializer after enabling of wavefrontparallel processing (WPP).
 17. The non-transitory computer-readablemedium of claim 13, wherein the predefined coding region is a CTU, andthe resetting is performed according to a palette predictor initializerafter enabling of wavefront parallel processing (WPP).
 18. Thenon-transitory computer-readable medium of claim 13, wherein thedetermining the palette for the block is performed independently ofpalette information of blocks in another predefined coding region thatis decodable in parallel with the predefined coding region.